The invention is generally related to the field of inline power delivery.
Electronic systems make use of inline power delivery to provide electrical operating power using the same conductors that are also used to carry data or information. Systems in use today include those referred to as “power over Ethernet” (POE), in which 48 volt DC power is carried on the same unshielded twisted pairs used to carry high speed Ethernet digital communications signals of 10/100 Mb/s or 1 Gb/s.
Inline power systems including POE systems employ certain signaling prior to the application of full DC power to determine whether a valid powered device (PD) capable of receiving inline power is attached to the conductors of a power delivery channel. Various forms of such signaling are used. According to one family of published standards generally falling within IEEE standard 802.3 (including 802.3af and the newer 802.3at), this signaling includes a “detection” operation and a separate “classification” operation, both of which involve the application of a signaling voltage on the power delivery channel by a power sourcing equipment (PSE) and a responsive signaling current generated on the power delivery channel by the PD. The signaling is based on a “point to point” assumption, i.e., that the PSE is connected to at most one PD by the power delivery channel. During detection, the PD presents a predetermined detection resistance of 25 kOhms to the power delivery channel, which is detected by the PSE as a current of (Vdet/25 k) where Vdet is the value of a detection voltage applied by the PSE. During classification, the PD conducts one of a set of predetermined classification currents in response to a classification voltage, the classification current indicating a “class” to which the PD belongs in terms of its power needs.
US published patent application 2006/0100799 A1 discloses various configurations in which multiple PDs are powered from a PSE via a power delivery channel. FIG. 4A shows a device 50 which is a power tap dongle having a connector 52 for connection to a PSE and a connector 54 for connection to a PD. In one embodiment, a controller 58 provides an identity network signal back to a PSE coupled with first connector 52 so that inline power may be provided. The device 50 may be adapted to act as a PSE device to determine if an attached device at the connector 54 has an appropriate identity network so that inline power may be provided to it. The controller 58 handles the inline power negotiations for device 50. The device 50 may provide a connection to enable the PSE and a device attached to connector 54 to engage in communications to establish/adjust power levels.